Plasma display and method of producing phosphor used therein

ABSTRACT

The present invention relates to a plasma display device and to a method of producing a phosphor to be used for the device, that prevents the phosphor layer from deteriorating, and improves the luminance, life, and reliability, of a plasma display panel (PDP). The plasma display device is equipped with a plasma display panel in which a plurality of discharge cells are arranged, phosphor layers ( 110 R,  110 G,  110 B) in color corresponding to each discharge cell are disposed, and phosphor layers ( 110 R,  110 G,  110 B) are excited by ultraviolet light to emit light. Green phosphor layer ( 110 G) has a green phosphor including Zn 2 SiO 4 :Mn, the element ratio of zinc (Zn) to silicon (Si) at the proximity of its surface is  2/1 , which is the stoichiometric ratio, and the layer is positively charged or zero-charged.

This application is a U.S. National Phase Application of PCTInternational Application PCT/JP2004/014415.

TECHNICAL FIELD

The present invention relates to a plasma display device having phosphorlayers that are excited by ultraviolet light to emit light, and to amethod of producing a phosphor used for the device.

BACKGROUND ART

In recent years, plasma display devices using plasma display panels(hereinafter, referred to as “PDP” or “panel”) receive attention ascolor display devices that implement a large screen size, a thin body,and a light weight in displaying color images for computers, televisionsets, and the like.

A plasma display device displays full color by means of additive colormixing of so-called three primary colors (red, green, and blue). Fordisplaying full color, a plasma display device is provided with phosphorlayers that emit light in the three primary colors: red (R), green (G),and blue (B). Phosphor particles composing the phosphor layers areexcited by ultraviolet light occurring in a discharge cell of the PDP,to generate visible light in each color.

Compounds used for the above-mentioned phosphors in each color include(YGd)BO₃:Eu³⁺ and Y₂O₃:Eu³⁺ for emitting red light; Zn₂SiO₄:Mn²⁺ forgreen; and BaMgAl₁₀O₁₇:Eu²⁺ for blue. These phosphors, after given rawmaterials being mixed therewith, are produced with solid-phase reactionby being fired at a high temperature above 1,000° C. This method isdisclosed in “Phosphor Handbook (in Japanese)” (p. 219 to p. 220, byOhmsha, Ltd., 1991), for example.

The phosphor particles produced by firing, after being lightly crushedto the extent of breaking aggregated particles but not the crystals, arescreened (average particle diameter for red and green: 2 μm to 5 μm, forblue: 3 μm to 10 μm) before use. The reason for lightly crushing andscreening (classifying) phosphor particles is as follows: That is,methods of forming a phosphor layer in a PDP include screen-printing ofpasted phosphor particles in each color; and an ink-jet method, in whichthe paste is discharged through a nozzle for applying. Largeagglomerates are included in a phosphor unless the phosphor particlesare classified after being lightly crushed, and thus unevenness incoating and clogging in the nozzle may occur when coating with thepasted phosphors. Therefore, phosphors classified after being lightlycrushed are small in particle diameter and even in particle sizedistribution, thus yielding a more desirable coated surface.

An example method of producing a green phosphor made of Zn₂SiO₄:Mn isdisclosed in “Phosphor Handbook (in Japanese)” (pp. 219-220, Ohmsha,Ltd., 1991). That is, SiO₂ is blended in ZnO at the rate of 1.5ZnO/SiO₂,which is larger than its stoichiometric ratio (2ZnO/SiO₂), and thenfired in the air (one atmospheric pressure) at 1,200° C. to 1,300° C.,to produce a green phosphor. Therefore, the surface of the Zn₂SiO₄:Mncrystal is covered with an excessive amount of SiO₂, and the phosphorsurface is negatively charged.

The fact that a green phosphor in a PDP, negatively charged with a highlevel, degrades in its discharge characteristic, is disclosed inJapanese Patent Unexamined Publications No. H11-86735 and No.2001-236893, for example. Further, it is known that ink-jet coating, inwhich coating is made continuously using negatively charged ink for agreen phosphor through a fine-bore nozzle, causes clogging in the nozzleand unevenness in coating. These are because ethyl cellulose in the inkis in particular presumably resistant to being adsorbed in the surfaceof the negatively charged green phosphor.

Further, there is a problem in which a negatively charged phosphorcauses ion collision of positive ions of Ne, CH-base, or H occurringwhile discharging with a negatively charged green phosphor, thusdeteriorating the luminance of the phosphor.

Meanwhile, some methods are formulated such as laminate-coatingpositively charged oxide for changing a negative charge on the surfaceof Zn₂SiO₄:Mn to a positive one, and mixing a positively charged greenphosphor for apparently positive charge. However, it is problematic thatlaminate-coating oxide causes a low luminance, and applying twodifferent kinds of phosphor with a charge state different from eachother tends to generate clogging and unevenness in coating. In addition,there is a method in which ZnO and SiO₂ are blended in advance at theratio of 2:1 or more (2/1 or more of Zn/Si in element ratio) whenproducing Zn₂SiO₄:Mn, and ZnO is scattered (sublimed) in advance whilefiring, utilizing the vapor pressure of ZnO higher than SiO₂, whenfiring the phosphor in the air or in nitrogen at 1 atmospheric pressureat 1,200° C. to 1,300° C. However, even in such a case, the proximity ofthe crystal surface results in rich SiO₂ and negative charge by allmeans.

The present invention, in view of these problems, aims at preventingphosphor layers from deteriorating and at improving the luminance, life,and reliability of a PDP.

SUMMARY OF THE INVENTION

In order to achieve this purpose, a plasma display device of the presentinvention is equipped with a plasma display panel in which a pluralityof discharge cells are arranged, phosphor layers are disposed with acolor corresponding to each discharge cell, and the phosphor layers areexcited by ultraviolet light to emit light. The phosphor layers includea green phosphor layer containing Zn₂SiO₄:Mn, and the green phosphormade of Zn₂SiO₄:Mn has the element ratio of zinc (Zn) to silicon (Si) of2/1 in stoichiometric ratio at the proximity of the surface.

According to such a makeup, phosphor particles in which the greenphosphor crystal is positively charged or zero-charged allow thephosphor layer to be formed with an even coating, prevent the luminancedegradation of the phosphor, and improve the luminance, life, andreliability of the PDP.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a state of a PDP with its front glasssubstrate removed, used for a plasma display device according to anembodiment of the present invention.

FIG. 2 is a perspective view illustrating the structure of the imagedisplay area of the PDP.

FIG. 3 is a block diagram of the plasma display device according to theembodiment of the present invention.

FIG. 4 is a sectional view illustrating the structure of the imagedisplay area of the PDP used for the plasma display device according tothe embodiment of the present invention.

FIG. 5 is a schematic block diagram of an ink dispenser used whenforming a phosphor layer of the PDP.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the present invention, the element ratio of zinc (Zn) to silicon (Si)at the proximity of the surface of the green phosphor made of Zn2SiO4:Mnis assumed to be 2/1, which is the stoichiometric ratio. Further, theproximity of the surface of the green phosphor is positively charged orzero-charged. After ZnO, SiO₂, and MnO₂ as an activator are mixed, themixture is pre-fired in the air at 600° C. to 900° C., and then fired at1,000° C. to 1,350° C. in an atmosphere with 1 atmospheric pressure orhigher (0.105 MPa or higher) including at least one of N₂, N₂—O₂, andAr—O₂, to produce Zn2SiO4:Mn.

The green phosphor made of Zn₂SiO₄:Mn, used for a PDP, is usuallyproduced with a solid-phase reaction method, where SiO₂ is blended inZnO at a rate larger than its stoichiometric ratio, for improvingluminance. This results in the surface of the Zn₂SiO₄:Mn crystal beingcovered with SiO₂. However, even if produced in the stoichiometric ratioso that the surface will not be covered with SiO₂, firing at 1,000° C.or higher causes ZnO at the proximity of the surface to be scattered(sublimed) early, due to the vapor pressure of ZnO being higher thanthat of SiO₂, resulting in more SiO₂ on the surface of the phosphor. Iffired at 1,000° C. or lower so that ZnO will not be scattered(sublimed), although Zn₂SiO₄:Mn with its Zn/Si ratio of 2/1 issynthesized, a high-luminance phosphor is not produced due to its lowcrystallinity.

The present invention solves the above-mentioned problems with thefollowing method. That is, set the element ratio of ZnO to SiO₂ to beblended, to its stoichiometric ratio (2.0/1), and then fire in anatmosphere with its pressure between 0.105 MPa (1 atmospheric pressure)and 150 MPa, more desirably, between 1 MPa and 100 MPa, including N₂(nitrogen), N₂—O₂ (nitrogen-oxygen), or Ar—O₂ (argon-oxygen) in order toprevent the ZnO from being scattered (sublimed).

First, a description will be made for a method of producing a phosphoraccording to the present invention.

Methods of producing a phosphor body itself include the following. Thatis, one method is solid-phase sintering, where an oxidized or carbonatedraw material, and flux are used. Another is method liquid-phase method,where a precursor of a phosphor is produced with hydrolysis oforganometallic salt or nitrate salt in an aqueous solution, or withcoprecipitation that precipitates organometallic salt or nitrate saltwith alkali or the like added, and then the precursor is heat-treated toproduce pre-fired powder. Yet another method is liquid spraying, wherean aqueous solution with raw materials for a phosphor added is sprayedinto a heated oven.

According to the present invention, with a phosphor precursor andpre-fired powder produced with any of the above methods, the dischargecharacteristic is improved and clogging in the nozzle is eliminated, asa result of using a green phosphor made of Zn₂SiO₄:Mn produced by firingin an atmosphere with its pressure between 1 and 1,500 atmosphericpressures (between 0.105 MPa and 152 MPa) including at least one of N₂,N₂—O₂, and Ar—O₂.

First, a description will be made for a method of producing Zn₂SiO₄:Mnwith a solid-phase reaction method. After blending carbonate and oxideas the raw materials, such as ZnO, SiO₂, and MnCO₃, with the molar ratioof the base material [(Zn_(1-x)Mn_(x))₂SiO₄] for a phosphor, pre-firethem at 600° C. to 900° C. for 2 hours. Next, slightly crush and screenthem, and then actually fire them in an atmosphere with its pressurebetween 1 and 1,500 atmospheric pressures (between 0.105 MPa and 152MPa) including N₂, N₂—O₂, or Ar—O₂ at 1,000° C. to 1,350° C., to form agreen phosphor.

Alternatively, in a liquid-phase method, where a phosphor is producedfrom an aqueous solution, the following process is employed. That is,dissolve organometallic salt (e.g. alkoxide, acetylacetone) or nitratesalt, into water in advance so that the element ratio of Zn/Si will be2.0/1, which is the stoichiometric ratio of Zn₂SiO₄:Mn. Next, hydrolyzeit to produce a coprecipitate (hydrate), and pre-fire it at 600° C. to900° C. in the air. After that, actually fire it in an atmosphere withits pressure between 1 atmospheric pressure and 1,500 atmosphericpressure (153 MPa), more desirably between 0.105 MPa and 150 MPa,including at least one of N₂, N₂—O₂, and Ar—O₂, at 1,000° C. to 1,350°C. for 2 to 10 hours, and then classify it to produce a green phosphor.

In a green phosphor produced in this way, that is, by firing in anatmosphere with its pressure higher than 0.105 MPa including at leastone of N₂, N₂—O₂, and Ar—O₂, at 1,000° C. to 1,350° C., ZnO is notscattered (sublimed) from the surface of the phosphor particles.Therefore, Zn₂SiO₄:Mn with Zn is produced that is even in its densityextending from the surface to the inside of the phosphor. This resultsin a green phosopher with Zn₂SiO₄:Mn particles having an improved chargecharacteristic.

The reason for limiting the pressure when firing between 1 and 1,500atmospheric pressures, more desirably between 0.105 MPa and 150 MPa, isthat ZnO cannot be prevented from being scattered (sublimed) at 0.105MPa or lower; the production cost becomes too high at 150 MPa or higher.

Next, a description will be made for a phosphor in each color used for aplasma display device according to the present invention. Concretephosphor particles used for a green phosphor layer are desirably thosemade from [(Zn_(1-x)Mn_(x))₂SiO₄] as their parent body, produced withthe aforementioned method, and the value of x desirably satisfies0.01≦x≦0.2 for advantages in luminance and luminance degradation.

As concrete phosphor particles for a blue phosphor layer, a compoundexpressed by Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) orBa_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) can be used. Here, the values x and yof the compound desirably satisfy 0.03≦x≦0.20, and 0.1≦y≦0.5,respectively, for high luminance.

As concrete phosphor particles for a red phosphor layer, a compoundexpressed by Y_(2x)O₃:Eu_(x) or (Y, Gd)_(1-x)BO₃:Eu_(x) can be used.Here, the value x of the compound for a red phosphor desirably satisfies0.05≦x≦0.20, for advantages in luminance and luminance degradation.

Hereinafter, a description will be made of an embodiment of a plasmadisplay device according to the present invention, with reference to thedrawings.

FIG. 1 is a plan view illustrating a state of a PDP with its front glasssubstrate removed, used for the plasma display device according to theembodiment of the present invention. FIG. 2 is a perspective viewillustrating the structure of the image display area of the PDP. Here,FIG. 1 shows display electrodes, display scan electrodes, and addresselectrodes, with some of them omitted so as to be easily understood.

As shown in FIG. 1, PDP 100 is composed of front glass substrate 101(not illustrated), rear glass substrate 102, N pieces of displayelectrodes 103, N display scan electrodes 104 (N is affixed for showingthe Nth one), a group of M pieces of address electrodes 107 (M isaffixed for showing the Mth one), and hermetic seal layer 121 shown byoblique lines. PDP 100 has an electrode matrix with a three-electrodestructure composed of display electrode 103, display scan electrode 104,and address electrode 107; and a display cell is formed at theintersecting point of display electrode 103 and display scan electrode104, and address electrode 107, forming image display area 123.

This PDP 100, as shown in FIG. 2, is composed of a front panel withdisplay electrode 103, display scan electrode 104, dielectric glasslayer 105, and MgO protective layer 106, all disposed on one mainsurface of front glass substrate 101; and a back panel with addresselectrode 107, dielectric glass layer 108, barrier rib 109, and phosphorlayers 110R, 110G, and 110B, all disposed on one main surface of rearglass substrate 102. PDP 100 has a structure in which discharge gas isencapsulated in discharge space 122 formed between the front and backpanels, and is connected to PDP driver 150 shown in FIG. 3, to compose aplasma display device.

As shown in FIG. 3, the plasma display device has display driver circuit153, display scan driver circuit 154, and address driver circuit 155,all in PDP 100. A discharge voltage is applied to display scan electrode104 and address electrode 107 corresponding to a cell to be emitted,under control of controller 152, to perform address discharge betweenthe electrodes. After that, a pulse voltage is applied between displayelectrode 103 and display scan electrode 104 to perform sustaindischarge. This sustain discharge causes ultraviolet light to occur at arelevant cell. A phosphor layer excited by this ultraviolet light emitslight, to light the cell, where a combination of emitted and non-emittedcells in each color displays an image.

Next, a description will be made for a method of producing theabove-mentioned PDP 100, referring to FIGS. 4 and 5. FIG. 4 is asectional view illustrating the structure of the image display area ofthe PDP used for the plasma display device according to the embodimentof the present invention. In FIG. 4, the front panel is produced in thefollowing way. That is, after forming display electrode 103 and displayscan electrode 104, N pieces each (Only two pieces each are shown inFIG. 2.), alternately and parallel in a striped form on front glasssubstrate 101, cover the top of them with dielectric glass layer 105,and further form MgO protective layer 106 on the surface of dielectricglass layer 105.

Display electrode 103 and display scan electrode 104 are composed of atransparent electrode made of indium tin oxide (ITO) and a bus electrodemade of silver. The bus electrode is formed from the silver paste beingapplied with screen-printing and then fired.

Dielectric glass layer 105 is formed from a paste including a lead-basedglass material being applied with screen-printing and then fired at agiven temperature for a given time (at 560° C. for 20 minutes, forexample), so that the layer will have a given thickness (approximately20 μm). A paste including the above-mentioned lead-based glass materialis, for example, a mixture of PbO (70 wt %), B₂O₃ (15 wt %), SiO₂ (10 wt%), Al₂O₃ (5 wt %), and an organic binder (10% ethyl cellulose dissolvedin alpha-terpineol). Here, an organic binder means a resin dissolved inan organic solvent, where an acrylic resin, besides ethyl cellulose, canbe used as a resin, and butylcarbitol or the like can be also used as anorganic solvent. Further, such an organic binder may immix glyceryltrileate, for example.

MgO protective layer 106, made of magnesium oxide (MgO), is formed witha method such as sputtering or chemical vapor deposition (CVD) so thatthe layer will have a given thickness (approximately 0.5 μm).

The back panel is formed from a silver paste for electrodes beingscreen-printed onto rear glass substrate 102 and then fired, into astate where M pieces of address electrodes 107 are installed in a row. Apaste including a lead-based glass material is applied on the back panelwith screen-printing, to form dielectric glass layer 108. In the sameway, a paste including a lead-based glass material is applied repeatedlyat a given pitch with screen-printing and then fired, to form barrierrib 109. This barrier rib 109 partitions discharge space 122 line-wiseinto each cell (unit of light-emitting region). W, which is the gapbetween barrier ribs 109, is defined as between approximately 130 μm and240 μm according to high-definition TV with its screen size between 32inches and 50 inches.

Phosphor layers made of phosphor particles in red (R), blue (B), andgreen (G) are formed between barrier ribs 109, where the green particlesare produced by firing the material with its element ratio of Zn/Si of2.1/1 to 2.0/1, in an atmosphere with its pressure higher than 1atmospheric pressure (0.102 MPa) including at least one of N₂, N₂—O₂,and Ar—O₂.

Phosphor layers 110R, 110G, and 110B, where phosphor particles are boundeach other, are formed from a phosphor ink paste made of phosphorparticles and an organic binder being applied and then fired at 400° C.to 590° C. to burn out the organic binder.

It is desirable to form phosphor layers 110R, 110G, and 110B, so that L,which is the lamination-wise thickness of the layers on addresselectrode 107, will be roughly 8 to 25 times the average particlediameter of the phosphor particles in each color. In other words, thephosphor layer desirably retains a thickness of at least 8 layers, andpreferably about 20 layers of lamination, in order not to letultraviolet light generated in the discharge space transmit but to beeliminated, for ensuring luminance (emission efficiency) whenirradiating the phosphor layer with a certain amount of ultravioletlight. This is because the emission efficiency of the phosphor layer isalmost saturated, and the size of discharge space 122 cannot beadequately ensured with a thickness of more than about 20 layers.

Meanwhile, phosphor particles which are small enough in their diameterand are spherical, such as those produced with a hydrothermal synthesismethod or the like, raise the filling density of the phosphor layers andincrease the total surface area of the phosphor particles, as comparedto the case of unspherical particles and the same levels of lamination.

The front and back panels produced in this way are overlap each other sothat respective electrodes on the front panel will be orthogonalizedwith the address electrodes on the back panel. In addition, the panelsare sealed with sealing glass inserted to the periphery of the panels,and then fired at approximately 450° C. for 10 to 20 minutes, forexample, to form hermetic seal layer 121. Next, after the inside ofdischarge space 122 is once exhausted to a high vacuum (e.g. 1.1×10⁻⁴Pa), discharge gas such as an He—Xe-based or He—Xe-based inactive gas isencapsulated at a given pressure, producing PDP 100.

FIG. 5 is a schematic block diagram of ink dispenser 200 used whenforming phosphor layers 110R, 110G, and 110B. As shown in FIG. 5, inkdispenser 200 includes server 210, pressure pump 220, and header 230.Phosphor ink supplied from server 210 for storing phosphor ink,pressurized by pressure pump 220, is supplied to header 230. Header 230is provided with ink chamber 230 a and nozzle 240, and the pressurizedphosphor ink supplied to ink chamber 230 a is discharged continuouslythrough nozzle 240. D, which is the bore of this nozzle 240, isdesirably 30 μm or larger for preventing clogging in the nozzle, and isdesirably equal to W (approximately 130 μm to 200 μm) or less, where Wis the gap between barrier ribs 109, for preventing the nozzle fromprotruding from barrier rib 109 when applying, where it is set usuallybetween 30 μm to 130 μm.

Header 230 is linearly driven by a header scanning mechanism (notillustrated). Having header 230 scan as well as continuously dischargingphosphor ink 250 through nozzle 240 allows the phosphor ink to beuniformly applied to the grooves between barrier ribs 109 on rear glasssubstrate 102. Here, the viscosity of the phosphor ink used ismaintained between 1,500 centipoise (CP) and 50,000 CP at 25° C.

Still, above-mentioned server 210 is equipped with an agitation device(not illustrated), which prevents the particles in the phosphor ink frombeing precipitated. Header 230 is integrally molded with ink chamber 230a including nozzle 240, and is produced from a metallic material withmachining and electric discharging.

Further, a method of forming a phosphor layer is not limited to theabove-mentioned one, but various methods can be used such as aphotolithographic method, screen-printing, and a method in which a filmwith phosphor particles mixed is disposed.

Phosphor ink is a mixture of phosphor particles in each color, a binder,and solvent, all blended so that the viscosity will range between 1,500centipoise (CP) and 50,000 CP, where a surface active agent, silica,dispersant (0.1 wt % to 5 wt %), and others may be added as required.

A red phosphor blended in this phosphor ink is a compound expressed by(Y, Gd)_(1-x)BO₃:Eu_(x) or Y_(2x)O₃:Eu_(x). These are compounds in whichEu is substituted for a part of Y element composing its maternalmaterial. Here, x, which is the substitution value of Eu element for Yelement, is desirably in the range of 0.05≦x≦0.20. For a substitutionvalue more than this, the luminance significantly degrades although itincreases, which is assumed to be impractical. Meanwhile, for asubstitution value less than this, the composition ratio of Eu, which isthe main element of light-emitting, decreases, as well as the luminance,thus making it useless as a phosphor.

A green phosphor uses a compound expressed by [(Zn_(1-x)Mn_(x))₂SiO₄]that has been fired in an atmosphere with its pressure higher than 1atmospheric pressure (0.102 MPa) including at least one of N₂, N₂—O₂,and Ar—O₂. [(Zn_(1-x)Mn_(x))₂SiO₄] is a compound in which Mn issubstituted for a part of Zn element composing its maternal material.Here, x, which is the substitution value of Mu element for Zn element,ia desirably in the range of 0.01≦x≦0.20.

A blue phosphor uses a compound expressed by Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) orBa_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x). Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) andBa_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) are compounds in which Eu or Sr issubstituted for a part of Ba element composing its maternal material.Here, x and y, which are substitution values of Eu element for Baelement, is desirably in the range of 0.03≦x≦0.20 and 0.1≦y≦0.5.

As a binder blended in a phosphor ink, ethyl cellulose or acrylic resin(0.1 wt % to 10 wt % of ink is mixed) can be used; and as a solvent,alpha-terpineol or butylcarbitol can be used. Here, the binder may bepolymer molecules such as PMA or PVA, and the solvent may be an organicsolvent such as diethylene glycol or methyl ether.

In this embodiment, phosphor particles are manufactured with asolid-phase reaction method, an aqueous solution method, a spray firingmethod, or a hydrothermal synthesis method. A concrete example for amethod of producing phosphor particles will be hereinafter described.

First, a description will be made of a method of producing a bluephosphor of Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) with an aqueous solution method.

In the process of producing a mixed solution, mix the raw materials ofbarium nitrate Ba(NO₃)₂, magnesium nitrate Mg(NO₃)₂, aluminium nitrateAl(NO₃)₃, and europium nitrate Eu(NO₃)₂, with the molar ratio of1-x:1:10:x (0.03≦x≦0.25), and dissolve them into an aqueous medium toproduce a mixed solution. This aqueous medium is desirably ion-exchangedwater or pure water in that they do not include an impure substance;however, they can be used even if they include a nonaqueous solvent(e.g. methanol, ethanol). Next, put the hydrate liquid mixture into acontainer made of a material with resistance to corrosion and heat, suchas gold or platinum, and then use a device capable of heating underpressure, such as an autoclave, to perform hydrothermal synthesis (for12 to 20 hours) at a given temperature (100° C. to 300° C.), at a givenpressure (0.2 MPa to 10 MPa), in a high-pressure container. Next, firethis powder in a reducing atmosphere (e.g. atmosphere including 5% ofhydrogen and 95% of nitrogen) at a given temperature for a given time(e.g. at 1,350° C. for 2 hours), and classify this, to produce a desiredblue phosphor of Ba_(1-x)MgAl₁₀O₁₇:Eu_(x).

Phosphor particles produced with hydrothermal synthesis are sphericaland have particle diameters smaller than those produced with theconventional solid-phase reaction, resulting in an average particlediameter of approximately 0.05 μm to 2.0 μm. Here, “spherical” isdefined as the aspect ratio (minor axis diameter/major axis diameter) ofmost phosohor particles ranges between 0.9 and 1.0, for example, whereall the phosphor particles do not necessarily need to fall in thisrange.

Alternatively, a blue phosphor can be produced with spraying, in whichthe hydrate mixture is not put into a gold or platinum container, butthe mixture is sprayed through a nozzle to a high-temperature oven, tosynthesize a phosphor.

Next, a description will be made of a method of producing a bluephosphor of Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) manufactured with asolid-phase reaction method.

Weigh the raw materials of barium hydroxide Ba(OH)₂, strontium hydroxideSr(OH)₂, magnesium hydroxide Mg(OH)₂, aluminum hydroxide Al(OH)₃, andeuropium hydroxide Eu(OH)₂, for a required molar ratio, and mix themalong with AlF₃ as flux. After that, fire them at a given temperature(1,300° C. to 1,400° C.), for a given time (12 to 20 hours), to produceBa_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) in which quadrivalent ions aresubstituted for Mg and Al. The average particle diameter of the phosphorparticles produced with this method is approximately 0.1 μm to 3.0 μm.Next, after firing these particles in a reducing atmosphere, 5% hydrogenand 95% nitrogen, for example, at a given temperature (1,000° C. to1600° C.), for a given time (2 hours), classify them with an airclassifier to produce phosopher powder.

Here, oxide, nitrate salt, and hydroxide are mainly used as the rawmaterials for a phosphor. However, a phosphor can be produced also withan organometallic compound including elements such as Ba, Sr, Mg, Al,and Eu (e.g. metal alkoxide and acetylacetone).

Next, a description will be made of a green phosphor of(Zn_(1-x)Mn)₂SiO₄ produced with a solid-phase method.

First, mix the raw materials of zinc oxide (ZnO), silicon oxide (SiO₂),and manganese oxide MnO, so that the molar ratio of Zn to Mn will be, 1x:x (0.01≦x≦0.20), and next mix the raw materials along with flux (ZnF₂,MnF₂) as required, so that the element ratio of Zn to Si will be 2.1/1to 2.0/1. Pre-fire this mixture at 600° C. to 900° C. for 2 hours, andlightly crush the mixture to the extent of breaking the agglomerate.Next, fire this in an atmosphere with its pressure between 0.105 Mpa and150 MPa including at least one of N₂, N₂—O₂, and Ar—O₂, at 1,000° C. to1,350° C., to produce a green phosphor.

Next, a description will be made of the case where a green phosphor isproduced with an aqueous solution method.

First, in the process of producing a mixed solution, use the rawmaterials of zinc nitrate Zn(NO₃)₂, manganese nitrate Mn(NO₃)₂, andtetraethoxysilane [Si(O.C₂H₅)₄]. First, mix them, so that the molarratio of zinc nitrate to manganese nitrate will be 1-x:x (0.01≦x≦0.20).Next, in blending Zn(NO₃)₂ and [Si(O.C₂H₅)₄], mix the raw materials sothat the element ratio of Zn to Si will be 2.0/1, and put them intoion-exchanged water to produce a mixed solution.

Next, in a hydration process, drop a basic aqueous solution (e.g.aqueous ammonia solution) into this mixed solution to form hydrate.Then, pre-fire this hydrate at 600° C. to 900° C., and next fire thispre-fired matter in an atmosphere with its pressure higher than 0.105Mpa including at least one of N₂, N₂—O₂, and Ar—O₂, at 1,000° C. to1,350° C., for 2 to 20 hours, to produce a green phosphor.

Next, a description will be made of a method of producing a red phosphorwith an aqueous solution method.

First, a red phosphor of (Y, Gd)_(1-x)BO₃:Eu_(x) will be described. Inthe process of producing a mixed solution, mix the raw materials ofyttrium nitrate Y₂(NO₃)₃, hydro nitrate gadolinium Gd₂(NO₃)₃, boric acidH₃BO₃, and europium nitrate Eu₂(NO₃)₃, so that the molar ratio will be1-x:2:x (0.05≦x≦0.20) (The ratio of Y to Gd is 65:35.), and afterheat-treating them at 1,200° C. to 1,350° C. in the air for 2 hours,classify them to produce a red phosphor.

Meanwhile, for a red phosphor of Y_(2x)O₃:Eu_(x), in the process ofproducing a mixed solution, dissolve the raw materials of yttriumnitrate Y₂(NO₃)₂ and europium nitrate Eu(NO₃)₂ into ion-exchanged water,so that the molar ratio will be 2-x:x (0.05≦x≦0.30), to produce a mixedsolution. Next, in a hydration process, add a basic aqueous solution(e.g. aqueous ammonia solution) to this aqueous solution to formhydrate. After that, in hydrothermal synthesis process, put the hydrateand ion-exchanged water into a container with resistance to corrosionand heat, such as platinum or gold, and then perform hydrothermalsynthesis in a high-pressure container such as an autoclave, at 100° C.to 300° C. at a pressure between 0.2 MPa and 10 MPa for 3 to 12 hours.After that, dry the yielded compound to produce desired Y_(2x)O₃:Eu_(x).Next, after annealing this phosphor in the air at 1,300° C. to 1,400° C.for 2 hours, classify it to form a red phosphor.

EVALUATION EXPERIMENT

Hereinafter, in order to evaluate the performance of the plasma displaydevice according to the present invention, an evaluation experiment ismade for sample devices using phosphors according to the above-mentionedembodiment.

The respective plasma display devices are produced so that they willhave a 42-inch size (specification of high-definition TV with its ribpitch of 150 μm), the thickness of the dielectric glass layer is 20 μm,the thickness of the MgO protective layer is 0.5 μm, and the distancebetween the display electrode and display scan electrode is 0.08 mm. Thedischarge gas to be encapsulated in the discharge space is a neon-basedgas with a xenon gas mixed by 5%, encapsulated at a given discharge-gaspressure.

A total of 9 samples are produced for plasma display devices. In thesesamples, a [(Zn_(1-x)Mn_(x))₂SiO₄] phosphor produced at a pressure ashigh as between 0.105 Mpa and 150 Mpa is used for a green phosphor.Table 1 shows the conditions of synthesis and the methods of producingfor each phosphor used in these samples.

TABLE 1 Pre-Firing Atmosphere and Pressure in Sample Amount oftemperature temperature in actually Amount of Eu: Method of Amount ofMn: Method of number Mn: x (° C.) actually firing firing (Mpa) xmanufacturing x manufacturing Green phosphor [(Zn_(1.x)Mn_(x))₂SiO₄] Redphosphor Blue phosphor Solid-phase method [(Y, Gd)_(1.x)BO₃:Eu_(x)][Ba_(1.x)MgAl₁₀O₁₇:Eu_(x)] 1 x = 0.02 In the air, In N₂, 1,200° C., 20 x= 0.1 Solid-phase x = 0.1 Solid-phase 600° C., 3 hours reaction reaction2 hours method method 2 x = 0.05 In the air, In N₂—O₂ 150 x = 0.2 (sameas the x = 0.2 (same as the 750° C., 1,350° C., above) above) 2 hours 3hours 3 x = 0.1 In the air, In N₂, 1,150° C., 10 x = 0.3 (same as the x= 0.5 (same as the 850° C., 3 hours above) above) 2 hours 4 x = 0.2 Inthe air, In Ar—O₂, 0.105 x = 0.15 (same as the x = 0.1 (same as the 900°C., 1,000° C., above) above) 2 hours 10 hours Green phosphor[(Zn_(1.x)Mn_(x))₂SiO₄] Red phosphor Blue phosphor Liquid-phase method[(Y_(1.x))₂O₃Eu_(x)] [Ba_(1.x.y)Sr_(y)MgAl₁₀O₁₇:Eu_(x)] 5 x = 0.01 Inthe air, In N₂—O₂, 50 x = 0.01 Aqueous x = 0.2, Aqueous 700° C., 1,300°C., solution y = 0.1 solution 3 hours 3 hours method method 6 x = 0.03In the air, In Ar—O₂, (same as the x = 0.1 (same as the x = 0.3, (sameas the 800° C., 1,300° C., above) above) y = 0.3 above) 3 hours 10 hours7 x = 0.05 (same as the In N₂—O₂, (same as the x = 0.15 (same as the x =0.4, (same as the above) 1,300° C., above) above) y = 0.5 above) 3 hours8 x = 0.1 (same as the (same as the (same as the x = 0.2 Solid-phase x =0.5, (same as the above) above) above) reaction y = 0.3 above) method 9x = 0.05 (same as the (same as the (same as the (same as the (same asthe x = 0.15, (same as the above) above) above) above) above) y = 0.5above) 10* (same as (same as the (same as the 1 atmospheric (same as the(same as the (same as the (same as the the above) above) above) pressureabove) above) above) above) (0.101 Mpa) *Sample number 10 is for acomparative example.

Samples 1 through 4 are combinations of a green phosphor using(Zn_(1-x)Mn_(x))₂SiO₄ produced with a solid-phase synthesis method; ared phosphor, (Y, Gd)_(1-x)BO₃:Eu_(x); and a blue phosphor,(Ba_(1-x)MgAl₁₀O₁₇:Eu_(x)). Each sample shows variation in the method ofsynthesizing a phosphor; substitution ratios of Mn and Eu, which are themain elements for light-emitting, namely the substitution ratio of Mn toZn element and the substitution ratio of Eu to Y and Ba elements; andthe pressure in actually firing for a green phosphor, as shown in table1.

Samples 5 through 9 are combinations of a red phosphor using(Y_(1-x))₂O₃:Eu_(x); a green phosphor, (Zn_(1-x)Mn_(x))₂SiO₄ producedwith a liquid-phase method; and a blue phosphor,Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x). Each sample shows, in the same way asthe above, variation in the method of synthesizing a phosphor; and thepressure in actually firing for a green phosphor, as shown in table 1.

Phosphor ink used for forming a phosphor layer is produced by mixing aphosphor, resin, solvent, and dispersant, using each phosphor particleshown by table 1.

The measurement result shows that the viscosity of the phosphor ink atthat time (25° C.) all remains in the range between 1,500 CP and 50,000CP. In all the phosphor layers formed, the side faces of the barrierribs are found by observation to be uniformly coated with phosphor ink.

The bore of the nozzle used for coating then is 100 μm, and phosphorparticles used for phosphor layers have an average particle diameter of0.1 μm to 3.0 μm and a maximum particle size of 8 μm or less.

Sample 10 is a comparative sample where a green phosopher layer isformed using green phosopher particles with their surfaces negativelycharged, produced at 1 atmospheric pressure (0.101 Mpa), which is aconventional example.

Experiment 1

A measurement is made of the charging tendency for the green phosphorsin samples 1 through 9 and comparative sample 10. Here, the measurementadopts blow-off method, which measures the amount of charge for reducediron powder.

Experiment 2

A measurement is made of the element ratio of Zn to Si at the proximity(approximately 10 nm in depth) of the surface with X-Ray photoelectronspectroscopy (XPS) for samples 1 through 9 and comparative sample 10produced.

Experiment 3

A measurement is made of the luminance of a PDP when displaying fullwhite after the PDP producing process, and the luminance of green andblue phosphor layers, with a luminance meter.

Experiment 4

A measurement is made of the rate of luminance change when displayingfull white, green, and blue as follows: That is, apply discharge sustainpulses with 185 V, 100 kHz, to a plasma display device for 1,000 hourscontinuously, measure the luminance of the PDP before and after then,and calculate the luminance degradation factor (<[luminance afterapplication−luminance before application]/luminance beforeapplication>*100)

An address error during address discharge is judged from at least asingle flicker on the screen.

Experiment 5

Clogging in the nozzle is checked when green phosphor ink is appliedusing a nozzle with its bore of 100 μm, for 100 hours continuously.

Table 2 shows experimental results of the luminance and the rate ofluminance change in blue, and of clogging in the nozzle, in experiments1 through 5.

TABLE 2 Zn/Si ratio of Rate of luminance change green phosphor (%) ofpanel after discharge with XPS and Luminance sustain pulses with 185 V,Address charging tendency of panel in 100 kHz applied for 1,000 errorduring Clogging in Sample Zn/Si ratio green hours address nozzle (200number Charging endency Cd/cm2 Green Blue discharge hours) 1 2.0/1 251.0−1.0 −2.5 No No + 2 (same as the 268.0 −1.3 −2.3 (same as the (same asthe above) + above) above) 3 (same as the 274.0 −0.9 −2.4 (same as the(same as the above) 0 above) above) 4 (same as the 255.0 −1.1 −2.2 (sameas the (same as the above) 1 above) above) 5 2.0/1 242.0 −1.3 −2.2 (sameas the (same as the + above) above) 6 (same as the 257.0 −1.4 −2.5 (sameas the (same as the above) + above) above) 7 (same as the 273.9 −1.2−2.1 (same as the (same as the above) + above) above) 8 (same as the270.0 −1.5 −2.2 (same as the (same as the above) + above) above) 9 (sameas the 268.0 −1.6 −2.3 (same as the (same as the above) + above) above)10* 1.92/1 240.0 −28.3 −5.1 Yes Yes − *Sample number 10 is for acomparative example.

As shown in table 2, in comparative sample 10, which uses a greenphosphor made of negatively charged (Zn_(1-x)Mn_(x))₂SiO₄ produced withthe conventional producing method, a large luminance degradation factoris shown in green and blue in an accelerated life due to the negativecharge. Particularly, an accelerated life test in the condition of 185V, 100 kHz, and 1,000 hours, shows −28.3% of the rate of change indisplaying green. Meanwhile, in samples 1 through 9, where the surfaceof the green phosphors according to the present invention has itselement ratio of Zn/Si equal to its stoichiometric ratio and positivelycharged or zero-charged, the rate of change is as low as −0.9% to −1.6%.The rate of the change in luminance in blue is −5.1% in the comparativesample, while in samples 1 through 9, the rate is all between −2.1% and−2.5%, and an address error and clogging in the nozzle when applyingphosphors do not occur.

This is presumably because positively charging or zero-charging(Zn_(1-x)Mn_(x))₂SiO₄, which is a negatively charged green phosphor,causes the phosphor to be immune to an impact of positive ions such asneon ions (Ne⁺) and CH_(x)-based ions (CH_(x) ⁺) existing in thedischarge space of the panel, suppressing luminance degradation. Thereason why address errors have been eliminated is homogenization ofaddress discharge as a result that the green phosphor is positivelycharged, which is the same as for the red and blue ones. Still, thereason why clogging in the nozzle has been eliminated is presumably theimproved dispersibility of the phosphor ink because the ethyl cellulosein the binder is prone to adsorbing a positively charged green phosphor.

INDUSTRIAL APPLICABILITY

As above-mentioned, according to the present invention, a green phosphor(Zn_(1-x)Mn_(x))₂SiO₄ composing a phosphor layer is positively chargedor zero-charged, by being fired in an atmosphere with its pressurebetween 0.105 MPa and 150 MPa including at least one of N₂, N₂—O₂, andAr—O₂, to homogenize coating condition, to prevent deterioration, of thephosphor layer, and also to improve the luminance, life, andreliability, of a PDP, thus effectively improving the performance of theplasma display device.

1. A method of producing a phosphor for a plasma display device,comprising: a process in which one of metal salt, nitrate salt, andorganometallic salt, including zinc, silicon and manganese elementswhich comprise a green phosphor, are blended so that an element ratio ofZn to Si is to be 2/1, and then the salt and water are mixed to producemixed liquid; a pre-firing process in which, after the mixed liquid isdried, the mixed liquid is fired in an air at 600° C. to 900° C., toproduce pre-fired matter; and a firing process in which the pre-firedmatter is fired in an atmosphere including at least one of N₂, N₂—O₂,and Ar—O₂, between 0.105 MPa and 150 MPa inclusive, at 1,000° C. to1,350° C.
 2. A method of producing a phosphor for a plasma displaydevice, comprising: a process of mixing a raw material for a phosphor,in which a raw material of oxide and/or carbonate including zinc,silicon and manganese elements which comprise a green phosphor, aremixed; a pre-firing process in which the mixed raw material is fired inan air at 600° C. to 900° C., to produce pre-fired matter; and a firingprocess in which the pre-fired matter is fired in an atmosphereincluding at least one of N₂, N₂—O₂, and Ar—O₂, between 0.105 MPa and150 MPa inclusive, at 1,000° C. to 1,350° C.